Wednesday, 14 February 2018

More about birches

I often mention birches in my blog. They have to be among my favourite trees and I'm sure this is a sentiment I share with many others. Around sixty species of birch exist across the northern hemisphere but their fossil remains date back to Upper Cretaceous times, when dinosaurs still existed. 
Yesterday, strolling through the grounds of Northampton General Hospital, I was pleased to see some rather nice specimens of the Paper-bark Birch, Betula papyrifera. It is native to North America and the indigenous people there put it to good use for canoes, roofing (it is waterproof) and so on. The specimens I saw yesterday were in a rather inaccessible place and as a consequence the bark was peeling off in sheets of significant size. Normally, I suspect, people can't resist the temptation to tug at this loose material so sizeable pieces never survive.
Paper-bark Birches in the grounds of Northampton General Hospital.
12 February, 2018

Similar birch species occur in Asia and Hindu manuscripts, dating from around 1800 B.C., were written on birch bark. 'Birches are good biochemists' states Colin Tudge (Ref.1) and few would argue with that. Although birches are not in the same family as willows (the former are in the Betulacae whereas willows are placed in the Salicaceae) both contain aspirin-like compounds. In the case of birches the active compound is methyl salicylate which is present in oil wintergreen, also obtained from birches.They can be used to make syrups and in times of famine the starch and oils also present have possibly meant the difference between death and survival.
The fissured bark of silver birch. Beckett's Close, Byfield.
14 February, 2018
It is generally agreed that our two native oaks, Quercus robur and Q. petraea, support more insects than any other British trees. But the silver birch also does extremely well in this respect. From moths such as the Birch Mocha, Cyclophora albipunctata, to bugs like the Birch Shieldbug, Elasmostethus interstinctus it is host to a great array of organisms. Micro-moths in particular seem to occur on birches prolifically and at least nine species of aphids (Ref 2) may be found on their leaves and twigs.
A second birch species occurs in Northamptonshire, particularly on badly-drained soils. This is the Downy Birch, Betula pubescens, but this will have to be dealt with on another occasion.
Finally, the sap of birches, particularly that of Sweet Birch, Betula lenta, can be employed to make birch beer.
I like birches!

1. Tudge, Colin (2005) The Secret Life of Trees  Penguin Books

2. Dixon, T and Thieme, (2007) Aphids on Deciduous Trees  Richmond Publishing

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